Touch sensing apparatus

ABSTRACT

An apparatus and method for sensing touch between a compression mold and a workpiece located in the compression mold including a mold cavity and a mold closure movable relative to the workpiece. The apparatus may include at least one touch sensor pad positionable to signal touch between the mold closure and the workpiece. The touch sensor pad may be in communication with a touch sensor monitor for indicating touch between the workpiece and the mold closure. The touch sensor pad may also be embodied in a touch sensor assembly.

This application is a continuation of application Ser. No. 09/192,427,filed Nov. 16, 1998 now U.S. Pat. No. 6,294,113 which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to a touch sensor, and more specifically, toenhancing contact or pressure between a mold closure and a workpiece toprevent lateral movement of the workpiece during compression molding.

Typically, a multilayered workpiece is formed layer by layer, whereindividual layers can vary by at least 5-10% in thickness. The workpieceis then debulked by applying a vacuum and heat to remove gas andpre-densify the workpiece. Finally, the workpiece is placed in a sealedbag in a mold and further densified into a final formed workpiece usingonly autoclave air pressure. Compression molding a debulked workpiece,however, has been found to provide better exterior surface geometry thanconventional autoclave molding, as well as forcing the workpiece to afinal geometry which is less dependent on material layer variability.

In a compression molding process, the preformed workpiece is assembledsimilar to the autoclave process. Instead of autoclave molding theworkpiece for final densification, however, the debulked workpiece isplaced in a compression mold cavity and a mold closure moves intocontact with the workpiece while the mold is also heated according to apre-determined temperature schedule. Final densification of theworkpiece is performed by compressing the workpiece between the moldcavity and the mold closure within the mold.

Unfortunately, the act of obtaining better exterior surface geometrythrough compression molding may, in some cases, lead to the generationof excessive lateral flow of one or more layers of the workpiece. Theexcessive lateral flow may tend to form wrinkles in the one or morelayers. Such wrinkles create an abnormality in the workpiece and in somecases may lead to a derating of the strength of the final formedworkpiece.

One cause for the excessive lateral flow is believed to be non-uniformcontact between the mold and the workpiece, particularly upon initialcontact of the mold with the workpiece before compression moldingcommences. Another cause is believed to be non-uniform pressure appliedto the workpiece during compression molding. Consequently, it isdesirable to assure that the mold contacts the preformed workpiece ascompletely and uniformly as possible before and during compressionmolding to reduce the likelihood of excessive lateral motion of theworkpiece relative to the mold. For a similar reason, it is desirable toassure that the pressure applied upon the preformed workpiece duringcompression molding is tailored to get a high quality part.

Accordingly, there is a need in the art for an improved mold closure.

SUMMARY OF THE INVENTION

An apparatus and method is disclosed for sensing touch between acompression mold and a workpiece located in the compression moldincluding a mold cavity and a mold closure movable relative to theworkpiece. The apparatus may include at least one touch sensor padpositionable to signal touch between the mold closure and the workpiece.The touch sensor pad may be in communication with a touch sensor monitorfor indicating touch between the workpiece and the mold closure. Thetouch sensor pad may also be embodied in a touch sensor assembly.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic exploded cross-sectional side view of a moldclosure, a workpiece, a mold cavity and a touch sensor, where the moldclosure is moved into contact with the workpiece;

FIG. 2 is a non-exploded view of FIG. 1;

FIG. 3 is a diagrammatic partial plan view along the line 3—3 of FIG. 2,but including a plurality of touch sensors;

FIG. 4 is a schematic diagram of a compression mold, a compression moldcontrol system and a touch sensor monitor;

FIG. 5 is a diagrammatic cross-sectional side view of a portion of acontact type touch sensor pad;

FIG. 6 is a view similar to FIG. 5 but of an alternative embodiment ofthis invention;

FIG. 7 is a diagrammatic cross-sectional side view of a portion of astrain gauge type of pressure touch sensor pad;

FIG. 8 is a view similar to FIG. 7 but of an alternative embodiment ofthis invention comprising a piezoelectric type of pressure touch sensorpad;

FIG. 9 is a view similar to FIG. 7 but of another alternative embodimentof this invention comprising a capacitive type of pressure touch sensorpad;

FIG. 10 is a view similar to FIG. 7 but of yet another alternativeembodiment of this invention comprising a fiber optic type of pressuretouch sensor pad; and

FIG. 11 is a flow diagram depicting steps for practicing the invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1-3 diagrammatically illustrate an apparatus 10 for sensing touchbetween a mold 26, for example, a compression mold, and a workpiece 40,typically composed of multiple layers of material. Mold 26 may compriseany conventional compression molding machine that includes a compressionmold closure 30, a compression mold cavity 28 and a mold aperture 70leading from inside mold cavity 28 to an outside environment. In oneembodiment, mold 26 comprises a four-piston hydraulic type ofcompression mold machine, for example, a Murdock™ compression moldmachine.

Workpiece 40 can be positioned in mold cavity 28, which mold cavity 28is preferably substantially fixed relative to workpiece 40, and therebyworkpiece 40 is movable relative to mold closure 30. At least one touchsensor, such as touch sensor pad 12, is positionable to signal how moldclosure 30.touches workpiece 40. The term touch is used herein toinclude any force or effect from mold 26 on workpiece 40 or vice versa.Such touch could range from direct physical touch between opposingsurfaces of each to touch between opposing surfaces of each via at leastone intermediary means. Also, such touch could range from mere contact,as contact is defined herein, to pressure, as pressure is definedherein, between opposing surfaces of workpiece 40 and mold 26.

Referring to FIG. 5, preferably touch sensor 12 typically comprises atleast a contact sensor, such as a contact type touch sensor pad 14. Pad14 can generate a signal that indicates when compression mold closures30 contacts workpiece 40 as mold closure 30 is moved into positiontowards workpiece 40 and mold cavity 28 (FIG. 2). The term contact isused herein to include any contact between mold closure 30 and workpiece40 ranging from direct physical contact between opposing surfaces ofeach to contact between opposing surfaces of each via at least oneintermediary means. Although contact can be indicated at any time withthis invention, it is most useful to know when initial contact is madebetween mold closure 30 and workpiece 40. For example, the time of thisinitial contact can be usefully employed as “time-zero” to begin a twostep controlled process of (1) closing mold 26 and (2) starting the moldheating. Each step preferably has its own baseline schedule of closure(or preferred force exerted upon workpiece 40) and heat applications,respectively, from then on through completion of the molding process.Subsequent contacts across the surface of workpiece 40, however, canalso be used to modify these baseline schedules during the moldingprocess.

Referring to FIG. 7, additionally or alternatively, touch sensor 12 maycomprise a pressure sensor, such as a pressure type touch sensor pad 84.The pressure sensor can provide a signal that indicates a surfacepressure between workpiece 40 and compression mold closure 30 adjacentsensor 12, for example, local surface pressure. The term pressure isused herein to include any pressure between mold closure 30 andworkpiece 40 ranging from direct physical pressure between opposingsurfaces of each to pressure between opposing surfaces of each via atleast one intermediary means. Although pressure can be indicated at anytime with this invention, it is most useful to know what the localworkpiece surface pressure is throughout compression molding afterinitial contact between the mold closure and the workpiece.

Referring to FIG. 3, at least one sensor 12 preferably comprises aplurality of sensors 12 disposed to signal touch between mold closure 30and workpiece 40 at a plurality of different points across a surface 42of workpiece 40. As desired, each sensor 12 may include a contact sensoror pressure sensor, or both. Further, referring to FIG. 2, it ispreferred that mold closure 30 tilt relative to workpiece 40 to increasea total number of the plurality of different points signaling touchbetween mold closure 30 and workpiece 40. Tilting may be achievedthrough manipulation of mold closure 30 by manual or automatic means.Preferably, tilting is enabled in opposing directions 34 along at leastone diameter of mold 26 and most preferably along multiple diameters ofmold 26.

FIG. 4 schematically depicts compression mold 26, a compression moldcontrol system 36 and a touch sensor monitor 38. Each communicate withone another to operate mold 26 and monitor and interpret how moldclosure 30 is in touch with workpiece 40. For example, manual orautomatic means may be utilized to monitor touch between workpiece 40and mold closure 30 and also to interpret the signal towards controllingmovement of mold closure 30 based on the interpreted signal.

FIG. 5 diagrammatically illustrates contact type touch sensor pad 14,which pad 14 is positionable between mold closure 30 and workpiece 40.Contact type touch sensor pad 14 may comprise a touch sensor assembly 16including a compliant sheet material 18 and contact type touch sensorpad 14. For example, excellent results are contemplated when contacttype touch sensor pad 14 comprises a membrane switch used, for example,in appliance user interfaces. Such a low pressure sensor pad (e.g.,preferably <1 psi), gives a positive signal on contact with a very smalldeflection and can bear very high loads (i.e., while the contacts areclosed). Further, excellent results are contemplated when, for example,compliant sheet 18 comprises a non-conductive deformable member from thegroup consisting of resin, thermoplastic resin and silicone rubber, suchas GE Lexan™ polycarbonate, GE Ultrin™ polyetherimide or DuPont Kevlar™resins.

Still referring to FIG. 5, in touch sensor assembly 16 each contact typetouch sensor pad 14 (generally indicated by pads 12 in FIG. 3) may beconnected to a signal run 20 to provide communication from pad 14 tooutside of mold 26. For example, metal contact type touch sensor pads 14and metal signal runs (e.g., wires) 20 may be utilized for signalingcontact with a metal mold closure 30. In such a case, at least oneconventional touch sensor monitor, for example, an Ohm meter 72 (FIG.2), may be connected to signal runs 20 outside of mold 26. This mayinclude use of a wire connector junction 22 (FIG. 3) or signal runs 20may extend continuously uninterrupted from pads 14 to outside of mold26. In either case, signal runs 20 exit mold interior through moldaperture 70, or the like, including any of several conventional sealstructures such as elastomeric seals or fast cure seals that can bebroken off signal runs 20 when compression molding is completed.

In particular, when metal mold closure 30 comes in contact with contacttype touch sensor pads 14 (e.g., touch sensor pads 12 of FIG. 2comprising contact type touch sensor pads), pads 14 signal contact atone or more points across surface 42 of workpiece 40. That is, signalruns 20 may be sequentially connected to a low, DC voltage source whoseother terminal would be connected to metal mold closure 30. As moldclosure 30 moves toward workpiece 40, at least one, and then others andpreferably all, contact type touch sensor pad 14 closes the circuit in asimple continuity check arrangement. This information could beinterpreted, by conventional means, to determine which contact typetouch sensor pad(s) 14 contact mold closure 30. This information may inturn thereby provide direction to a manual operator or automatic controlsystem as to how to tilt mold closure 30 to enhance a touch result, forexample, contact, between mold closure 30 and workpiece 40.

FIG. 6 diagrammatically illustrates an alternative embodiment of acontact type touch sensor pad 76 and touch sensor assembly 16 of thisinvention. In this embodiment the sensor can be completely encapsulatedwithin compliant sheet material 18. Contact type touch sensor pad 76 canbe formed by two opposing surfaces of signal run 20 (for example, awire) spaced from each other by an insulator 24. Such a contact typetouch sensor pad 76 may further include a pair of nubs 56 whereinoutside pressure applied to nubs 56 presses them inward toward eachother and when their opposing surfaces contact, a circuit is completed,including wire run 20. Also, this embodiment need not be compatible withmold closure 30 (i.e., metal to metal, etc.) because contact type touchsensor pad 76 is wholly contained within compliant sheet material 18.Thus, this embodiment may merely depend on signal communication throughcontact type touch sensor pad 76 and signal run 20. Other than thesestructural distinctions, this embodiment is similar to contact typetouch sensor pad 14.

FIG. 7 diagrammatically illustrates a strain gauge pressure type touchsensor which is positionable between mold closure 30 and workpiece 40.This pressure type touch sensor may also comprise touch sensor assembly16 including compliant sheet material 18 and a pressure type touchsensor pad 80 or contact type touch sensor pad(s) 14 or 76, andpreferably both. Such a pressure sensor (e.g., preferably sensitive at10 psi to 1000 psi), more accurately measures local surface pressurebetween workpiece 40 and mold closure 30 throughout compression moldingof workpiece 40. Touch sensor of this invention may comprise a singlestructure having the features and pressure ranges desired for bothcontact type and pressure type touch sensors of the invention.

Still referring to FIG. 7, for example, excellent results arecontemplated when the pressure type touch sensor comprises a flat straingauge pad 80. Pad 80 may include a resistor 82 mounted on a deflectablebar or disc substrate 84. In use, bending substrate 84 changes theresistance measured by a resistance monitor 86, and this measurement canbe used to determine pressure differentials.

FIG. 8 diagrammatically illustrates another embodiment of a pressuretype touch sensor pad 90, which, aside from its particular function, isinterchangeable with the strain gauge type sensor (FIG. 7). Sensor pad90 may comprise a piezoelectric sensor pad. The sensor may includeelectrodes 92 plated on piezoelectric material 94. In use, changes inexternal pressure change the voltage measured by a conventional voltagemonitor 96, and this measurement can be used to determine pressuredifferentials.

FIG. 9 diagrammatically illustrates another embodiment of a pressuretype touch sensor pad which, aside from its particular function, isinterchangeable with the strain gauge type sensor (FIG. 7). Sensor pad100 illustrates a conventional capacitive sensor pad. The sensor mayinclude deformable material 104 between stiff conductors 102. In use, agap 106-106 reduces under loading and system capacitance increases, asmeasured by a capacitance monitor 108, and this measurement can be usedto determine pressure differentials.

FIG. 10 diagrammatically illustrates another embodiment of a pressuretype touch sensor pad 110 which, aside from its particular function, isinterchangeable with the strain gauge type sensor (FIG. 7). Sensor pad110 illustrates a fiber optic sensor pad. The sensor may include a fiberoptic sensor 114, with a phosphor coated tip 120, surrounded by a gel112 (e.g., silicone rubber) in a pressure-tight elastomeric bag 116. Inuse, changes in external pressure change the gel pressure on phosphortip 120 and fluorescent decay time as a function of pressure is measuredby a monitor 118. This measurement can be used to determine pressuredifferentials. For example, a Ruxtron CO.™ or Panametrics Co.™ fiberoptic pressure type touch sensor pad is contemplated to produceexcellent results.

FIG. 11 depicts a flow diagram for practicing the invention. Forexample, after a preformed workpiece 40 is debulked and placed in themold cavity 28 opposing the mold closure 30, at least one touch sensor12, and preferably a plurality of contact type and pressure type touchsensors, are positioned adjacent to workpiece 40 or mold closure 30, atstep 44. Next, mold closure 30 and workpiece 40 are moved, preferablyslowly, relative to one another (either or both moving, but preferablyonly mold closure 30 moving) and a signal is generated indicating howmold closure 30 touches workpiece 40, at step 46. As used herein, thesignal may comprise a single signal or multiple signals, either or bothbeing associated with a single touch sensor 12 or multiple touch sensors12 depending on the intended use.

The step 46 signal is then interpreted to produce an interpreted signal,by conventional means that may be manual or automatic as discussedabove, at step 48. Depending on the interpreted signal (e.g., indicatingcontact at one or more points across workpiece 40 surface), the movementof mold closure 30 is conventionally guided, manually or automaticallyas discussed above, by changing a rate of closure or tilting the same.Preferably, the interpreted signal and guided movement are utilizedtowards enhancing a touch result between workpiece 40 and mold closure30, for example, such as increasing the total number of the plurality ofdifferent points signaling contact between mold closure 30 and workpiece40, at step 52.

Alternatively, or additionally, workpiece 40 may then be compressionmolded, at step 54. Preferably, this may include substantiallypreventing lateral movement of workpiece 40, namely the individuallayers or material thereof, during compression molding. This may alsoinclude modifying the temperature of workpiece 40, by conventionalmeans, according to a desired temperature schedule as discussedpreviously, at step 74. For example, in addition to enhancing contactbetween workpiece 40 and mold closure 30 during compression molding, thesignal from step 46, or a second signal generated from touch sensor 12,may indicate a local surface pressure between workpiece 12 and moldclosure 30, at step 56, which may also depend on the temperature ofworkpiece 40.

The signal or second signal is then interpreted to produce a secondinterpreted signal, by conventional means that may be manual orautomatic as discussed above, at step 58. Depending on the secondinterpreted signal (e.g., indicating contact at one or more pointsacross the workpiece surface indicating what the local pressure is at asurface of workpiece 40), the movement of mold closure 30 is furtherconventionally guided, manually or automatically as discussed above, byfurther changing the rate of closure or tilting the same as donepreviously, at step 60. That is, preferably compression moldingcomprises compression molding workpiece 40 into a high quality part as aresult of the enhanced touch results between workpiece 40 and moldclosure 30, i.e., substantially no wrinkles, substantially full density,substantially no porosity and preferred geometric specifications, atstep 62. In this way, the touch result desired, e.g., maximizing contactbetween workpiece 40 and mold closure 30 or maintaining a desiredpressure at the surface of workpiece 40 in spite of thermal expansionduring molding, can be obtained.

Yet alternatively, or additionally, the uniform structural integrity ofthe surface of workpiece 40 opposing mold closure 30 is maintainedduring the whole process such that any touch upon workpiece 40 by touchsensor(s) 12 is negligible to the final formed workpiece, at step 64.For example, in the embodiment of FIG. 6, this may be achieved byconventional means for maintaining a uniform thickness to the touchsensor assembly 16 in an environment ranging from mere atmosphericpressure to the high pressures experienced during compression molding.In the embodiment of FIG. 5, for example, mold closure 30 may haverecesses (not shown) to receive the contact sensor pads 14 and otherwisemay also maintain a uniform thickness to touch sensor assembly 16similar to the embodiment of FIG. 6.

After the compression molding step is completed, final formed workpieceis removed from mold 26, at step 66. Then, preferably, touch sensor(s)12 or touch sensor assembly 16, is separated from at least workpiece 40,at step 68. Alternatively, or additionally, contact sensor(s) 14 mayalso be separated from mold closure 30. In either case, preferably touchsensor(s) 12, or the touch sensor assembly 16, is reusable from oneworkpiece to another, and most preferably from one mold 26 to another.

This invention may have an endless variety of uses for all kinds ofcompression molded devices. Presently though, excellent results arecontemplated when the invention is used to manufacture aircraft enginefan blades made of laminated sheets of epoxy resin reinforced byunidirectional carbon fiber tows.

As various possible embodiments may be made in the above invention foruse for different purposes and as various changes might be made in theembodiments above set forth, it is understood that all matters here setforth or shown in the accompanying drawings are to be interpreted asillustrative and not in a limiting sense.

While only certain features of the invention have been illustrated anddescribed, many modifications and changes will occur to those skilled inthe art. It is, therefore, to be understood that the appended claims areintended to cover all such modifications and changes as fall within thetrue spirit of the invention.

What is claimed is:
 1. Apparatus for sensing touch between a compressionmold and a workpiece located in said compression mold including a moldcavity and a mold closure movable relative to said workpiece,comprising: at least one compliant sensor sheet positionable to signaltouch between said mold closure and said workpiece; wherein at least onetouch sensor generates a signal that indicates when said mold closurecontacts a portion of said workpiece and controls the mold closure basedon said signal to contact said workpiece with said remaining portions ofsaid mold closure.
 2. The apparatus of claim 1, wherein said at leastone touch sensor comprises a plurality of touch sensors disposed tosignal touch between said mold closure and said workpiece at a pluralityof different points across a surface of said workpiece.
 3. The apparatusof claim 2, wherein said mold closure tilts relative to said workpieceand further comprises a compression mold control system that controls amold closure rate or a tilt of said mold closure based on said signalgenerated by said at least one touch sensor.
 4. The apparatus of claim3, wherein said at least one touch sensor further comprises a pressuresensor and in which a second signal further indicates a surface pressurebetween said workpiece and said mold closure.
 5. The apparatus of claim1, wherein said at least one touch sensor comprises a touch sensor padpositionable between said mold closure and said workpiece.
 6. Theapparatus of claim 1, wherein said at least one touch sensor comprises atouch sensor assembly including a compliant sheet and said touch sensorpad.
 7. The apparatus of claim 6, wherein said compliant sheet comprisesa non-conductive deformable member from said group consisting of resin,thermoplastic resin and silicone rubber.
 8. The apparatus of claim 1,wherein said at least one touch sensor is reusable from one workpiece toanother.